X-Git-Url: http://plrg.eecs.uci.edu/git/?p=c11tester.git;a=blobdiff_plain;f=snapshot.cc;h=66faacd8e445510f57c7714ce9ccd60a1ee95f3c;hp=5069a1cf1147cb7afb07035cbf607c69daa2c284;hb=a0aabd321ed9a43bd0ff4be0d9a7751138c01004;hpb=d775a7d6624fa14284c4a273d039bedd21a1f55c diff --git a/snapshot.cc b/snapshot.cc index 5069a1cf..66faacd8 100644 --- a/snapshot.cc +++ b/snapshot.cc @@ -106,10 +106,10 @@ mprot_snapshotter::~mprot_snapshotter() static void mprot_handle_pf(int sig, siginfo_t *si, void *unused) { if (si->si_code == SEGV_MAPERR) { - model_print("Real Fault at %p\n", si->si_addr); - print_trace(); + model_print("Segmentation fault at %p\n", si->si_addr); model_print("For debugging, place breakpoint at: %s:%d\n", __FILE__, __LINE__); + // print_trace(); // Trace printing may cause dynamic memory allocation exit(EXIT_FAILURE); } void* addr = ReturnPageAlignedAddress(si->si_addr); @@ -148,12 +148,12 @@ static void mprot_snapshot_init(unsigned int numbackingpages, sa.sa_sigaction = mprot_handle_pf; #ifdef MAC if (sigaction(SIGBUS, &sa, NULL) == -1) { - model_print("SIGACTION CANNOT BE INSTALLED\n"); + perror("sigaction(SIGBUS)"); exit(EXIT_FAILURE); } #endif if (sigaction(SIGSEGV, &sa, NULL) == -1) { - model_print("SIGACTION CANNOT BE INSTALLED\n"); + perror("sigaction(SIGSEGV)"); exit(EXIT_FAILURE); } @@ -190,6 +190,9 @@ static void mprot_add_to_snapshot(void *addr, unsigned int numPages) exit(EXIT_FAILURE); } + DEBUG("snapshot region %p-%p (%u page%s)\n", + addr, (char *)addr + numPages * PAGESIZE, numPages, + numPages > 1 ? "s" : ""); mprot_snap->regionsToSnapShot[memoryregion].basePtr = addr; mprot_snap->regionsToSnapShot[memoryregion].sizeInPages = numPages; } @@ -249,11 +252,37 @@ static void mprot_roll_back(snapshot_id theID) #define STACK_SIZE_DEFAULT (((size_t)1 << 20) * 20) // 20 mb out of the above 100 mb for my stack struct fork_snapshotter { + /** @brief Pointer to the shared (non-snapshot) memory heap base + * (NOTE: this has size SHARED_MEMORY_DEFAULT - sizeof(*fork_snap)) */ void *mSharedMemoryBase; + + /** @brief Pointer to the shared (non-snapshot) stack region */ void *mStackBase; + + /** @brief Size of the shared stack */ size_t mStackSize; + + /** + * @brief Stores the ID that we are attempting to roll back to + * + * Used in inter-process communication so that each process can + * determine whether or not to take over execution (w/ matching ID) or + * exit (we're rolling back even further). Dubiously marked 'volatile' + * to prevent compiler optimizations from messing with the + * inter-process behavior. + */ volatile snapshot_id mIDToRollback; - ucontext_t mContextToRollback; + + /** + * @brief The context for the shared (non-snapshot) stack + * + * This context is passed between the various processes which represent + * various snapshot states. It should be used primarily for the + * "client-side" code, not the main snapshot loop. + */ + ucontext_t shared_ctxt; + + /** @brief Inter-process tracking of the next snapshot ID */ snapshot_id currSnapShotID; }; @@ -266,14 +295,40 @@ static struct fork_snapshotter *fork_snap = NULL; * The bug was actually observed with the forkID, these variables below are * used to indicate the various contexts to which to switch to. * -* @savedSnapshotContext: contains the point to which takesnapshot() call should switch to. -* @savedUserSnapshotContext: contains the point to which the process whose snapshotid is equal to the rollbackid should switch to -* @snapshotid: it is a running counter for the various forked processes snapshotid. it is incremented and set in a persistently shared record +* @private_ctxt: the context which is internal to the current process. Used +* for running the internal snapshot/rollback loop. +* @exit_ctxt: a special context used just for exiting from a process (so we +* can use swapcontext() instead of setcontext() + hacks) +* @snapshotid: it is a running counter for the various forked processes +* snapshotid. it is incremented and set in a persistently shared record */ -static ucontext_t savedSnapshotContext; -static ucontext_t savedUserSnapshotContext; +static ucontext_t private_ctxt; +static ucontext_t exit_ctxt; static snapshot_id snapshotid = 0; +/** + * @brief Create a new context, with a given stack and entry function + * @param ctxt The context structure to fill + * @param stack The stack to run the new context in + * @param stacksize The size of the stack + * @param func The entry point function for the context + */ +static void create_context(ucontext_t *ctxt, void *stack, size_t stacksize, + void (*func)(void)) +{ + getcontext(ctxt); + ctxt->uc_stack.ss_sp = stack; + ctxt->uc_stack.ss_size = stacksize; + makecontext(ctxt, func, 0); +} + +/** @brief An empty function, used for an "empty" context which just exits a + * process */ +static void fork_exit() +{ + /* Intentionally empty */ +} + static void createSharedMemory() { //step 1. create shared memory. @@ -285,7 +340,7 @@ static void createSharedMemory() //Setup snapshot record at top of free region fork_snap = (struct fork_snapshotter *)memMapBase; - fork_snap->mSharedMemoryBase = (void *)((uintptr_t)memMapBase + sizeof(struct fork_snapshotter)); + fork_snap->mSharedMemoryBase = (void *)((uintptr_t)memMapBase + sizeof(*fork_snap)); fork_snap->mStackBase = (void *)((uintptr_t)memMapBase + SHARED_MEMORY_DEFAULT); fork_snap->mStackSize = STACK_SIZE_DEFAULT; fork_snap->mIDToRollback = -1; @@ -302,7 +357,7 @@ mspace create_shared_mspace() { if (!fork_snap) createSharedMemory(); - return create_mspace_with_base((void *)(fork_snap->mSharedMemoryBase), SHARED_MEMORY_DEFAULT - sizeof(struct fork_snapshotter), 1); + return create_mspace_with_base((void *)(fork_snap->mSharedMemoryBase), SHARED_MEMORY_DEFAULT - sizeof(*fork_snap), 1); } static void fork_snapshot_init(unsigned int numbackingpages, @@ -316,81 +371,56 @@ static void fork_snapshot_init(unsigned int numbackingpages, void *pagealignedbase = PageAlignAddressUpward(base_model_snapshot_space); model_snapshot_space = create_mspace_with_base(pagealignedbase, numheappages * PAGESIZE, 1); - //step 2 setup the stack context. - ucontext_t newContext; - getcontext(&newContext); - newContext.uc_stack.ss_sp = fork_snap->mStackBase; - newContext.uc_stack.ss_size = STACK_SIZE_DEFAULT; - makecontext(&newContext, entryPoint, 0); + /* setup an "exiting" context */ + char stack[128]; + create_context(&exit_ctxt, stack, sizeof(stack), fork_exit); + + /* setup the shared-stack context */ + create_context(&fork_snap->shared_ctxt, fork_snap->mStackBase, + STACK_SIZE_DEFAULT, entryPoint); /* switch to a new entryPoint context, on a new stack */ - model_swapcontext(&savedSnapshotContext, &newContext); + model_swapcontext(&private_ctxt, &fork_snap->shared_ctxt); /* switch back here when takesnapshot is called */ - pid_t forkedID = 0; snapshotid = fork_snap->currSnapShotID; - /* This bool indicates that the current process's snapshotid is same - as the id to which the rollback needs to occur */ - bool rollback = false; while (true) { + pid_t forkedID; fork_snap->currSnapShotID = snapshotid + 1; forkedID = fork(); if (0 == forkedID) { - /* If the rollback bool is set, switch to the context we need to - return to during a rollback. */ - if (rollback) { - setcontext(&(fork_snap->mContextToRollback)); - } else { - /*Child process which is forked as a result of takesnapshot - call should switch back to the takesnapshot context*/ - setcontext(&savedUserSnapshotContext); - } + setcontext(&fork_snap->shared_ctxt); } else { - int status; - int retVal; - - DEBUG("The process id of child is %d and the process id of this process is %d and snapshot id is %d\n", - forkedID, getpid(), snapshotid); - - do { - retVal = waitpid(forkedID, &status, 0); - } while (-1 == retVal && errno == EINTR); + DEBUG("parent PID: %d, child PID: %d, snapshot ID: %d\n", + getpid(), forkedID, snapshotid); + + while (waitpid(forkedID, NULL, 0) < 0) { + /* waitpid() may be interrupted */ + if (errno != EINTR) { + perror("waitpid"); + exit(EXIT_FAILURE); + } + } - if (fork_snap->mIDToRollback != snapshotid) { + if (fork_snap->mIDToRollback != snapshotid) exit(EXIT_SUCCESS); - } - rollback = true; } } } static snapshot_id fork_take_snapshot() { - model_swapcontext(&savedUserSnapshotContext, &savedSnapshotContext); + model_swapcontext(&fork_snap->shared_ctxt, &private_ctxt); DEBUG("TAKESNAPSHOT RETURN\n"); return snapshotid; } static void fork_roll_back(snapshot_id theID) { + DEBUG("Rollback\n"); fork_snap->mIDToRollback = theID; - volatile int sTemp = 0; - getcontext(&fork_snap->mContextToRollback); - /* - * This is used to quit the process on rollback, so that the process - * which needs to rollback can quit allowing the process whose - * snapshotid matches the rollbackid to switch to this context and - * continue.... - */ - if (!sTemp) { - sTemp = 1; - DEBUG("Invoked rollback\n"); - exit(EXIT_SUCCESS); - } - /* - * This fix obviates the need for a finalize call. hence less dependences for model-checker.... - */ + model_swapcontext(&fork_snap->shared_ctxt, &exit_ctxt); fork_snap->mIDToRollback = -1; }